The overall objective of this project is to study the sites of binding and the mechanism of action of purified gonadotropins, LH and FSH, in the mammalian testis. Studies are planned or in progress to determine the role of FSH, LH and other peptide hormones in the synthesis and maintenance of the LH receptor; and their role in the regulation of synthesis of testosterone and other androgens. We are also studying the relationship of concentration of LH receptors to testicular responsiveness to LH.